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Old 02-08-2013, 10:01 AM   #1
mojopin74
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Fender Hot Rod Deville 4x10 1996 - Running amp at 4 Ohms instead of 8 Ohms.

Hi,

I’ve searched high and low on the internet trying to get some, what I presumed, would be relatively straight forward information, but have thus far not succeeded!

Hopefully, someone can assist me?

I have returned to guitar playing in the last 6-months after a lengthy sabbatical and my question is quite simple: What is/are the difference(s) of running the Fender Hot Rod Deville 4x10 at 4 ohms instead of 8 ohms?

Unfortunately my electrical knowledge and knowledge of tubes / valves is close to zero.

I have recently had an amp technician undertake a full re-tube and bias but wasn’t entirely happy with the results tone wise, although the clarity and sparkle has been restored. Subsequently, I have been researching the subject of tubes and am in the process of experimenting (though only with the Pre-amp tubes).

I am trying to warm up my tone a little but primarily obtain more clean headroom, as for some reason my amp can be quite harsh, cold and spikily abrasive sounding when it gets to gig volume (which doesn’t involve rotating the volume dial very far!).

Prior to trying different tubes (e.g. 12AY7 in V1 and / or perhaps 12AT7 in V3), I decided to try plugging into input ‘2.’ This provided some improvement (though I’ve often used Input 2 in the past anyway). I then thought, “why not try running at 4ohms instead of 8ohms?” I subsequently inserted a jack plug into the main speaker socket and moved the speaker lead over to the slave output to activate the 4 Ohms tap. The tone, to my ears anyway, was dramatically improved!

I’d just like to understand what the differences are and why I may have experienced an improvement in tonal quality? Is it simply the lower impedance, the 4Nr speakers (8 ohms) not being worked as hard? In addition is the amplifier drawing more power from the wall (just thinking about the ecological aspects!)?

Any assistance would be much appreciated!

Thanks & regards,

Neil.
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Old 02-08-2013, 10:50 AM   #2
Dave_Mc
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i think it's meant to be 8 ohms (don't quote me on that- just because fender says it's 8 ohms doesn't mean it is, i think they have form with running mismatches) so running into 4 ohms should actually drop your output power a little. you get maximum efficiency/power transfer when the impedances match.

i'm sure some of the other guys here could answer better than I could.
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Old 02-08-2013, 10:56 AM   #3
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Well you are presenting the amp with a mismatch... That's not good for the amp. How 'not good' it is is debatable, and I'm not knowledgable enough to start that debate, but if it were me I simply wouldn't risk it.

I think the issues you are experiencing can be solved in a way that doesn't risk harm to the amp. A 12AT7 in V3 would probably be my first choice, followed by new speakers. Honestly the Deville is a pretty lackluster amp in my opinion, your complaints are about what I would say about the amp.
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Old 02-08-2013, 03:08 PM   #4
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Quote:
Originally Posted by mojopin74
I have returned to guitar playing in the last 6-months after a lengthy sabbatical and my question is quite simple: What is/are the difference(s) of running the Fender Hot Rod Deville 4x10 at 4 ohms instead of 8 ohms?


i am assuming you want a little more insight here. this stuff confused me a bunch when i started too.

basically the output of your amp have an incredibly high output impedance, in order for the speakers to properly connect to the speakers (this has to do with circuit design and proper loading of the output, it's complicated) then tube guitar amps generally have to use an output transformer (OT).

the OT's job is just to take the high impedance of the power tubes and change it to a lower impedance that can match the speaker's impedance. it does this through taking advantage of inductance properties of electricity, which basically means they run an electrical current through a series of wires that are would very close to one another.

so what is the difference between the 4 ohm setting and the 8 ohm setting? the number of 'turns' of wire you are utilizing in the OT.

most likely your speakers in the HRD are set up for 8 ohms, so if you are just using the stock speakers then you should set it to 8 ohms. if you want to use another cabinet out of the HRD then you can get another 8 ohm cabinet, hook it to the jack on the bottom of the chassis and select 4 ohm output for the amp (two 8 ohm cabinets in parallel is 4 ohms). that is why you can choose between 8 or 4 ohms on there, so you can run another cabinet.

Quote:
Originally Posted by mojopin74
I have recently had an amp technician undertake a full re-tube and bias but wasn’t entirely happy with the results tone wise, although the clarity and sparkle has been restored. Subsequently, I have been researching the subject of tubes and am in the process of experimenting (though only with the Pre-amp tubes).

I am trying to warm up my tone a little but primarily obtain more clean headroom, as for some reason my amp can be quite harsh, cold and spikily abrasive sounding when it gets to gig volume (which doesn’t involve rotating the volume dial very far!).


i had the 4x10 deville for a bit too, i ran a 12AT7 in the V2 slot for a while to help tame that volume knob problem you are having. you can also replace the Master and Gain pots with a log taper pot instead of a linear taper pot it comes with stock. this provides much more range.

Quote:
Originally Posted by mojopin74
Prior to trying different tubes (e.g. 12AY7 in V1 and / or perhaps 12AT7 in V3), I decided to try plugging into input ‘2.’ This provided some improvement (though I’ve often used Input 2 in the past anyway). I then thought, “why not try running at 4ohms instead of 8ohms?” I subsequently inserted a jack plug into the main speaker socket and moved the speaker lead over to the slave output to activate the 4 Ohms tap. The tone, to my ears anyway, was dramatically improved!


that is interesting. this is how sweet water recommends connecting speaker to a HR series amp

Quote:
Originally Posted by Sweet Water
Hot Rod Speakers
02/19/2009

Q: Can I use an extension speaker with my Fender Hot Rod Deluxe amplifier without using the built-in speaker?

A: Yes, in fact, there are three ways to connect external speakers. The Hot Rod Deluxe has two speaker outputs, the main one, which is by default connected to the internal speaker, and the external speaker jack. Both of these are found on the bottom of the chassis, inside the amp enclosure.

The first thing to do is to unplug the internal speaker from the main speaker jack. Now you have your choice of three options:

1) Plug an 8-ohm speaker into the main speaker jack.

2) Plug two 8-ohm speakers in, one into the main speaker jack and one into the extension speaker jack.

3) Plug a 4-ohm speaker into the extension speaker jack. But in order to do so, you must also insert an "open" plug in the main speaker jack (a plug that's not connected to a speaker), so that the proper impedance is maintained.


if you aren't observing one of these methods of hooking the speaker up, then you are not running your amp properly.

Quote:
Originally Posted by mojopin74
I’d just like to understand what the differences are and why I may have experienced an improvement in tonal quality? Is it simply the lower impedance, the 4Nr speakers (8 ohms) not being worked as hard? In addition is the amplifier drawing more power from the wall (just thinking about the ecological aspects!)?

Any assistance would be much appreciated!

Thanks & regards,

Neil.


there is no way to explain why this sounds better to you. i could make up some new-age mumbo jumbo that could sound about right, but truthfully explaining why things 'sound good' is not a constructive exercise cuz there is there is no way to prove or disprove what you like. it is better off just noting that you liked it.

if you aren't matching the speaker's impedance to the amp's output impedance then you are causing additional stress in the operation of your amp. you may like that sound.

i don't see any reason your amp would be pulling more power from the wall either.
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Old 02-09-2013, 05:24 AM   #5
mojopin74
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Thanks for your replies. With regards to a mismatch, as far as the speakers are concerned, I'm not sure whether this is necessarily the case. In the Fender manual I managed to download, it suggests a solution almost identical to that suggested by Sweetwater i.e. inserting an open jack into the main speaker output and then re-connecting the amp speakers to the 'slave,' additional cabinet output. This appears to resolve that issue by virtue of the fact that, as far as the amp is concerned, the speakers receive 4 ohms, as they would if there was a cabinet attached.

I'm concerned that whilst the Fender manual depicts the configuration and annotates it by clarifying that an open jack is required to the main speaker output, it doesn't provide any further enlightenment!

Consequently, I'm just concerned about what is happening power wise. The transformer automatically switches, but surely it still receives the same input power supply to 'send' on to an attached cabinet and, thus, how is this power dissipated?

The change does seem to have helped with clarity, reduced the perceived volume and smoothed off some of the rough edges.

Yesterday evening, I tried a 12AY7 in V1; I expected a tonal change and volume reduction. The former was very subtle, the latter was quite dramatic (as anticipated) and I was virtually there clean headroom wise. I then added in the 12AT7 to V3 for devilment. Further, though subtle, apparent volume reduction, however, dramatic tonal difference!

It sounds a little bit more dark and possibly Marshall like, but I think I like it!

Unfortunately, I'm still quite confused and not sure of the full potential ramifications of my experimentation.

Can anybody shed any more light?

Once again, thanks for your efforts!

Cheers,

Neil.
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Old 02-09-2013, 11:00 AM   #6
gumbilicious
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Quote:
Originally Posted by mojopin74
Unfortunately, I'm still quite confused and not sure of the full potential ramifications of my experimentation.


i thought we did a pretty good job of explaining things.

the trasformer expects a certain nominal impedance to be supplied.

you are mismatching the impedance

you like the sound of the mismatched impedance.

i am sure it is a mismatch if your amp is a 4x10 deville, because the manual says so

Quote:
Originally Posted by manual
EXTERNAL SPEAKER - Plug-in connection for
an external speaker. This jack is wired in parallel
with the main speaker jack and must ONLY be used
in conjunction with the main speaker jack. If this
jack is used without the main speaker jack, there will
be no sound. The external speaker jack must be
used with an 8 ohm speaker enclosure for the Hot
Rod DeVille.
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Old 02-09-2013, 11:10 AM   #7
yousef213
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With tube amps You CAN mismatch IF the ohms of the speaker is LESS THAN the ohms of the output. If the speaker has more ohms than your amp it will blow your OT. Also although it is possible, it causes some strain on your tubes, so it is still ideal to match impedence
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Old 02-09-2013, 12:02 PM   #8
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I'm no electronics whizz and need to pay someone to fix my screwups so I like my impedances to match.

If your amp sounds like crap at the right impedance (too trebly,) you probably don't have speakers that suit you well. I have a few cabs around here and there's a giant difference to be had from them when used with the same head, an enormous difference.

I've found that a little more preamp gain will take the edge off of needle-sharp sounds. Maybe try using a 12AX7 where a 12AT7 is called for. I did that with my old Twin. It used to feel like a knitting needle in the ear at volume but now it's a bit less distinct and thus softer on the ears.
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Old 02-11-2013, 05:58 AM   #9
mojopin74
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Thanks for your help people!

I've compromised for the moment with a 12AY7 in V1, A 12AX7 in V2 and a 12AT7 in V3 with the amp back at 8 ohms.

It's subtle nuances, but it just sounds a bit tighter and punchier than it did at 4 ohms, were it sounded a fraction more rounded and warm. I rather not damage the transformer though and / or end up needing to re-tube umpteen times a year!

Do the output valves have any major influence on tone, or am I possibly looking at different speakers or trading the amp in!?

Regards,

Neil.
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Old 02-11-2013, 12:02 PM   #10
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based on my limited experience, power tubes can certainly affect the overall tone. whether they're the place to start, though, i dunno. normally speakers make a bigger difference than tubes.
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Old 02-11-2013, 12:31 PM   #11
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If it were a 1x12 or 1x10 I'd be inclined to suggest trying a speaker swap... But in a 4x10 that's probably not going to be cost-effective. Really that's going to be the biggest improvement you can make and I don't think the improvement is going to justify the cost. By the time you replace four ten inch speakers with high quality ones you could damn near buy another amp and keep the Deville as is.

Unless you are mostly happy with the tone but want to make a few tweaks, which doesn't sound like the case, then I'd say you need a new amp.
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Old 02-11-2013, 03:36 PM   #12
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^ that's a good point about the 4 speakers, i forgot about that. granted some 10" speakers aren't *that* dear (eminence legends, say), but yeah. even with cheap speakers that'll add up pretty quickly.
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Old 02-11-2013, 04:01 PM   #13
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Quote:
Originally Posted by Dave_Mc
^ that's a good point about the 4 speakers, i forgot about that. granted some 10" speakers aren't *that* dear (eminence legends, say), but yeah. even with cheap speakers that'll add up pretty quickly.

Bare minimum you're looking at $60 a speaker, before shipping... So take that $240 and add it to the ~$450 that amp would bring on Craigslist fairly easily, and you've got almost $700. Lots of great amps out there for $700 used.
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Old 02-12-2013, 02:13 PM   #14
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^ yep, when you put it like that...
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Old 02-12-2013, 02:27 PM   #15
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Quote:
Originally Posted by mojopin74
Do the output valves have any major influence on tone, or am I possibly looking at different speakers or trading the amp in!?


if you are having problems with the amp being too loud then the culprit is the linear taper knobs on the amp*, if you replace the stock knobs with audio taper knobs then you should get acceptable volume management.

* - i am assuming you have the 2nd gen of the amp. the newest generation uses the right knobs, but a common problem with the 2nd gen of the amp was the linear taper pots.
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